Hanna Instruments HI 3221 Instruction Manual page 13

ORP MEASUREMENTS
To perform ORP measurements, connect an ORP electrode (see "Accessories"
section) to the instrument and turn it ON.
If necessary, enter the mV mode by pressing RANGE
until the display changes to mV.
Submerse the ORP electrode 3 cm (1¼") into the sample
to be tested and wait a few seconds for the reading to
3 cm
stabilize.
Measurements are displayed with 0.1 mV resolution.
The "ATC" (or "MTC") message is turned off because mV readings are not
temperature compensated.
For accurate ORP measurements, the surface of the electrode must be clean
and smooth. Pretreatment solutions are available to condition the electrode
and improve its response time (see "Accessories" section, page 61).
RELATIVE mV MEASUREMENTS
To enter Relative mV mode, press Rel mV function key while in mV measure-
ment mode. The relative mV reading will be displayed along with the Absolute
mV value and the current temperature readings.
The relative mV reading is equal to the difference between the absolute mV
input value and relative mV offset established in the relative mV calibration.
Note: If using the pH or ISE electrode while in mV mode, the instrument will
measure the mV generated by the electrode.
ISE MEASUREMENTS (HI 3221, HI 3222 only)
To perform ion concentration measurements, connect an ISE electrode (and
the corresponding reference if necessary) to the corresponding instrument
input and turn it ON.
On HI 3222 the instrument input must be Channel 2. Press Channel, if
necessary, to display ISE in top header.
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